Since I didn‘t address the aesthetics and my practical preference in my previous post, let me add that:

I think the PP is one of the most elegant pistols ever designed. The PPK looks like a PP was forcibly shrunk, and the grip is a lot less comfortable even if you don‘t have particularly large hands. So from a purely practical point, the PPK/S is preferable to a PPK, but I‘d rather get an old PP any day.

Of course as others have described, the PPK/S has no history or significance as a service pistol or cultural icon at all, compared to the PP and PPK.